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3 October 2005Change 1, 1 September 2012

UNIFIED FACILITIES CRITERIA (UFC)

DESIGN: MOORINGS

APPROVED FOR PUBLIC RELEASE; DISTRIBUTION UNLIMITED

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DESIGN: MOORINGS

Any copyrighted material included in this UFC is identified at its point of use.Use of the copyrighted material apart from this UFC must have the permission of the copyrightholder.

U.S. ARMY CORPS OF ENGINEERS

NAVAL FACILITIES ENGINEERING COMMAND (Preparing Activity)

AIR FORCE CIVIL ENGINEER SUPPORT AGENCY

Record of Changes (changes are indicated by \1\ ... /1/)

Change No. Date Location

1 1 Sept 2012 3-2.5, 3-2.6, 3-3.1, 3-4, 3-6, 3-8, 3-8.8, 4-5.1, 6-8, 6-9,6-11, 7-4, 7-9, 8-3.3, 8-4.3, 8-5, 11-3, App A; minoreditorial corrections throughout

This UFC supersedes Mil itary Handbook 1026/4, dated July 1999.

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FOREWORD

The Unified Facilities Criteria (UFC) system is prescribed by MIL-STD 3007 and providesplanning, design, construction, sustainment, restoration, and modernization criteria, and applies

to the Military Departments, the Defense Agencies, and the DoD Field Activities in accordancewithUSD (AT&L) Memorandumdated 29 May 2002. UFC will be used for all DoD projects andwork for other customers where appropriate. All construction outside of the United States is alsogoverned by Status of Forces Agreements (SOFA), Host Nation Funded ConstructionAgreements (HNFA), and in some instances, Bilateral Infrastructure Agreements (BIA.)Therefore, the acquisition team must ensure compliance with the most stringent of the UFC, theSOFA, the HNFA, and the BIA, as applicable.

UFC are living documents and will be periodically reviewed, updated, and made available tousers as part of the Services responsibility for providing technical criteria for militaryconstruction. Headquarters, U.S. Army Corps of Engineers (HQUSACE), Naval FacilitiesEngineering Command (NAVFAC), and Air Force Center for Engineering and the Environment

(AFCEE) are responsible for administration of the UFC system. Defense agencies shouldcontact the preparing service for document interpretation and improvements. Technical contentof UFC is the responsibility of the cognizant DoD working group. Recommended changes withsupporting rationale should be sent to the respective service proponent office by the followingelectronic form: Criteria Change Request. The form is also accessible from the Internet siteslisted below.

UFC are effective upon issuance and are distributed only in electronic media from the followingsource:

Whole Building Design Guide web sitehttp://dod.wbdg.org/.

Hard copies of UFC printed from electronic media should be checked against the current electronicversion prior to use to ensure that they are current.

AUTHORIZED BY:

______________________________________DONALD L. BASHAM, P.E.Chief, Engineering and Construction DivisionU.S. Army Corps of Engineers

______________________________________DR. JAMES W WRIGHT, P.E.Chief EngineerNaval Facilities Engineering Command

______________________________________KATHLEEN I. FERGUSON, P.E.

The Deputy Civil EngineerDCS/Installations & LogisticsDepartment of the Air Force

______________________________________Dr. GET W. MOY, P.E.

Director, Installations Requirements andManagement

Office of the Deputy Under Secretary of Defense(Installations and Environment)
http://www.wbdg.org/pdfs/ufc_implementation.pdfhttp://www.wbdg.org/pdfs/ufc_implementation.pdfhttp://www.wbdg.org/pdfs/ufc_implementation.pdfhttp://www.wbdg.org/ccb/browse_cat.php?o=29&c=4http://www.wbdg.org/ccb/browse_cat.php?o=29&c=4http://dod.wbdg.org/http://dod.wbdg.org/http://dod.wbdg.org/http://dod.wbdg.org/http://www.wbdg.org/ccb/browse_cat.php?o=29&c=4http://www.wbdg.org/pdfs/ufc_implementation.pdf

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NEW DOCUMENT SUMMARY SHEET

Description of Change: The UFC 4-159-03, DESIGN: MOORING represents another step inthe joint Services effort to bring uniformity to the planning, design and construction of piers andwharves. This UFC contains extensive modifications in the following areas:

Heavy Weather Mooring Passing Ship Effects Ship Generated Waves Conversion from Mil-Hdbk to UFC and general updates and revisions

Reasons for Change: The existing guidance was inadequate for the following reasons: Need to convert to UFC format Incorporation of changes described above Update to referenced documents

Impact: The following direct benefits will result from the update of 4-159-03, DESIGN:MOORING:

Although primarily a U.S. Navy document, a single, comprehensive, up to datecriteria document exists to cover mooring design.

Eliminates misinterpretation and ambiguities that could lead to design andconstruction conflicts.

Facilitates updates and revisions and promotes agreement and uniformity of designand construction between the Services.

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TABLE OF CONTENTSPage

CHAPTER 1 INTRODUCTIONParagraph 1-1 Purpose and Scope ............................................................. 1

1-2 Purpose of Criteria ................................................................. 11-3 Definition ................................................................................ 11-4 Cancellation ........................................................................... 11-5 Organizational Roles and Responsibilities ............................. 1

CHAPTER 2 MOORING SYSTEMSParagraph 2-1 Introduction ........................................................................... 3

2-1.1 Purpose of Mooring ............................................................... 32-2 Types of Mooring Systems .................................................... 32-2.1 Fixed Mooring Systems ......................................................... 32-2.2 Fleet Mooring Systems .......................................................... 4

CHAPTER 3 BASIC DESIGN PROCEDUREParagraph 3-1 Design Approach ................................................................... 15

3-2 General Design Criteria ........................................................ 173-2.1 Mooring Service Types .......................................................... 183-2.2 Facility Design Criteria for Mooring Service Types ................ 193-2.3 Ship Hardware Design Criteria for Mooring Service Types .... 203-2.4 Strength ................................................................................. 203-2.5 Serviceability .......................................................................... 203-2.6 Design Methods ..................................................................... 233-2.7 General Mooring Integrity ...................................................... 23

3-2.8 Quasi-Static Safety Factors ................................................... 233-2.9 Allowable Ship Motions .......................................................... 233-3 Design Methods ..................................................................... 283-3.1 Quasi-Static Design ............................................................... 283-3.2 Dynamic Mooring Analysis..................................................... 293-4 Risk ..................................................................................... 293-5 Coordinate Systems .............................................................. 293-5.1 Ship Design/Construction Coordinates .................................. 323-5.2 Ship Hydrostatics/Hydrodynamics Coordinates ..................... 323-5.3 Local Mooring Coordinate System ......................................... 323-5.4 Global Coordinate System ..................................................... 32

3-5.5 Ship Conditions ..................................................................... 323-6 Vessel Design Considerations ............................................... 363-7 Facility Design Considerations............................................... 363-8 Environmental Forcing Design Considerations ...................... 383-8.1 Winds .................................................................................... 383-8.2 Wind Gust Fronts ................................................................... 413-8.3 Storms ................................................................................... 463-8.4 Currents ................................................................................. 48

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3-8.5 Water Levels .......................................................................... 483-8.6 Waves.................................................................................... 483-8.7 Water Depths......................................................................... 493-8.8 Environmental Design Information ......................................... 49

3-9 Operational Considerations ................................................... 503-10 Inspection .............................................................................. 503-11 Maintenance .......................................................................... 513-12 General Mooring Guidelines .................................................. 52

CHAPTER 4 STATIC ENVIRONMENTAL FORCES AND MOMENTS ON VESSELSParagraph 4-1 Scope .................................................................................... 55

4-2 Engineering Properties of Water and Air ............................... 554-3 Principal Coordinate Directions ............................................. 564-4 Static Wind Forces/Moments ................................................. 564-4.1 Static Transverse Wind Force ............................................... 56

4-4.2 Static Longitudinal Wind Force .............................................. 654-4.3 Static Wind Yaw Moment ...................................................... 694-5 Static Current Forces/Moments ............................................. 724-5.1 Static Transverse Current Force ............................................ 724-5.2 Static Longitudinal Current Force for Ships ........................... 794-5.3 Static Longitudinal Current Force for Blunt Vessels .............. 834-5.4 Static Current Yaw Moment ................................................... 834-6 Wind and Current Forces and Moments on Multiple Ships ... 84

CHAPTER 5 ANCHOR SYSTEM DESIGN PROCEDURESParagraph 5-1 General Anchor Design Procedure ........................................ 85

5-2 Drag-Embedment Anchor Specification ................................. 905-3 Driven-Plate Anchor Design .. ............................................... 96

CHAPTER 6 FACILITY MOORING EQUIPMENT GUIDELINESParagraph 6-1 Introduction ............................................................................ 99

6-2 Key Mooring Components ..................................................... 996-2.1 Tension Members .................................................................. 996-2.2 Compression Members.......................................................... 996-3 Anchors ................................................................................. 996-4 Chain and Fittings .................................................................. 1036-5 Buoys ..................................................................................... 107

6-6 Sinkers ................................................................................... 1076-7 Mooring Lines ........................................................................ 1076-7.1 Synthetic Fiber Ropes ........................................................... 1076-7.2 Wire Ropes ............................................................................ 1146-8 Fenders ................................................................................. 1146-9 Pier Fittings ............................................................................ 1166-10 Catenary Behavior ................................................................. 1196-11 Sources of Information .......................................................... 122

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CHAPTER 7 VESSEL MOORING EQUIPMENT GUIDELINESParagraph 7-1 Introduction ............................................................................ 123

7-2 Types of Mooring Equipment ................................................. 123

7-3 Equipment Specification ........................................................ 1237-4 Fixed Bitts .............................................................................. 1237-5 Recessed Shell Bitts .............................................................. 1247-6 Exterior Shell Bitts ................................................................. 1247-7 Chocks ................................................................................... 1247-8 Allowable Hull Pressures ....................................................... 1247-9 Sources of Information for Ships Mooring Equipment .......... 124

CHAPTER 8 EXAMPLE PROBLEMSParagraph 8-1 Introduction ............................................................................ 131

8-2 Single Point Mooring - Basic Approach ................................. 131

8-2.1 Background for Example ....................................................... 1338-2.2 Ship ..................................................................................... 1338-2.3 Forces/Moments .................................................................... 1338-2.4 Quasi-Static Design ............................................................... 1338-2.5 Mooring Hawser Break .......................................................... 1348.3 Fixed Mooring - Basic Approach ............................................ 1378-3.1 Background ........................................................................... 1378-3.2 Goal ..................................................................................... 1378-3.3 Ship ..................................................................................... 1378-3.4 Forces/Moments .................................................................... 1378-3.5 Definitions .............................................................................. 137

8-3.6 Preliminary Analysis .............................................................. 1378-3.7 Wharf Mooring Concept ......................................................... 1438.4 Spread Mooring - Basic Approach ......................................... 1488-4.1 Background for Example ....................................................... 1488-4.2 Goal ..................................................................................... 1488-4.3 Ship ..................................................................................... 1488-4.4 Forces/Moments .................................................................... 1508-4.5 Anchor Locations ................................................................... 1518-4.6 Definitions .............................................................................. 1528-4.7 Number of Mooring Legs ....................................................... 1528-4.8 Static Analysis ....................................................................... 154

8-4.9 Dynamic Analysis .................................................................. 1548-4.10 Anchor Design ....................................................................... 1578-5 Mooring LPD-17, LHD-1 and LHA-1 ...................................... 1618-5.1 Mooring LPD-17 ..................................................................... 161

CHAPTER 9 PASSING SHIP EFFECTS ON MOORED SHIPSParagraph 9-1 Introduction ............................................................................ 171

9-2 Passing Ship Effects on Moored Ships .................................. 171

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CHAPTER 10 SHIP WAVESParagraph 10-1 Introduction ............................................................................ 175

10-2 Ship Waves ........................................................................... 175

CHAPTER 11 HEAVY WEATHER MOORING GUIDELINESParagraph 11-1 Introduction ............................................................................ 179

11-2 Discussion ............................................................................. 17911-3 Heavy Weather Mooring Guidelines ..................................... 18011-4 Action ..................................................................................... 18511-4.1 Planning ................................................................................. 18511-4.2 Analysis and Design .............................................................. 18511-4.3 Maintenance .......................................................................... 18511-4.4 Operations ............................................................................. 18511-5 Environmental Design Criteria for Selected Sites .................. 185

GLOSSARY ................................................................................ 187

APPENDIX A REFERENCES/BIBLIOGRAPHY........................................... 189

FIGURESFigure Title Page

1-1 DOD Organizations Involved With Ship Moorings ............................. 2

2-1 Single Ship, Offset From a Pier With Camels .................................... 5

2-2 Ship at a T-Pier (plan view) ............................................................... 52-3 Floating Drydock Spud Moored ......................................................... 62-4 Ships on Both Sides of a Pier (plan view) ......................................... 62-5 Two Ships on One Side of a Pier (plan view) ................................... 72-6 Ship at Anchor ................................................................................... 92-7 Single Point Mooring With Drag Anchors .......................................... 102-8 Single Point Mooring With a Plate Anchor and a Sinker .................... 112-9 Bow-Stern Mooring Shown in Plan View .......................................... 122-10 Med-Mooring ..................................................................................... 122-11 Spread Mooring ................................................................................. 132-12 Two Inactive Ships Moored at a Wharf .............................................. 14

2-13 Spread Mooring ................................................................................. 14

3-1 Risk Diagram ..................................................................................... 313-2 Ship Design and Hydrostatic Coordinates ........................................ 333-3 Local Mooring Coordinate System for a Ship .................................... 343-4 Local Mooring Coordinate System for a Ship .................................... 353-5 Ratio of Wind Speeds for Various Gusts ........................................... 393-6 Typhoon OMAR Wind Chart Recording ............................................. 40

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3-7 Sample Wind Gust Fronts on Guam .................................................. 423-8 Distribution of Guam Wind Gust Front Wind Angle Changes ............ 433-9 Initial Versus Maximum Wind Speeds for Wind Gust Fronts ............. 443-10 Wind Gust Front Maxima on Guam 1982-1986 ................................. 45

3-11 Idealized Models of Chain Wear ........................................................ 52

4-1 Definition of Terms ............................................................................ 574-2 Local Coordinate System for a Ship .................................................. 584-3 Sample Ship Profiles ......................................................................... 614-4 Shape Function for Transverse Wind Force ...................................... 624-5 Example ..................................................................................... 644-6 Blockage Effect for an Impermeable Structure Next to a Moored Ship 654-7 Sample Yaw Normalized Moment Coefficient .................................... 714-8 Examples of Ratios of Ship Draft (T) to Water Depth (d) .................. 734-9 Broadside Current Drag Coefficient ................................................... 74

4-10 Example of Transverse Current Drag Coefficients ............................ 78

5-1 Example of a Drag-Embedment Anchor(Stabilized Stockless Anchor) ......................................................... 86

5-2 Example of a Drag-Embedment Anchor (NAVMOOR Anchor) ......... 875-3 Driven-Plate Anchor ........................................................................... 885-4 Anchor System Holding Capacity in Cohesive Soil (Mud) ................ 945-5 Anchor System Holding Capacity in Cohesionless Soil (Sand) ........ 955-6 Major Steps of Driven-Plate Anchor Installation ................................ 97

6-1 Chain Fittings ..................................................................................... 106

6-2 Synthetic Line Stretch ........................................................................ 1106-3 SEA-GUARD Fender Information ...................................................... 1156-4 SEA-CUSHON Fender Performance ................................................. 1166-5 Pier and Wharf Mooring Fittings Shown in Profile and Plan Views .... 1186-6 Sample Catenary ............................................................................... 1206-7 Load/Deflection Curve for the Example Mooring Leg ........................ 121

7-1 Fixed and Recessed Shell Bitts ......................................................... 1267-2 Recessed Shell Bitt (minimum strength requirements) ..................... 128

8-1 Some Types of Behavior of Ships at Single Point Moorings .............. 132

8-2 Example Single Point Mooring ........................................................... 1358-3 Example Mooring Failure Due to a Wind Gust Front ......................... 1368-4 Wind Forces and Moments on a Single Loaded CVN-68 for a

75-mph (33.5-m/s) Wind .................................................................. 1398-5 Definitions ..................................................................................... 1408-6 Optimum Ideal Mooring ..................................................................... 1418-7 Required Mooring Capacity Using the Optimum Ideal Mooring ......... 142

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8-8 Efficiency of Ship Moorings Using Synthetic Lines at Piers andWharves ..................................................................................... 144

8-9 CVN-68 Wharf Mooring Concept (Model 2) .................................... 1458-10 Component Analysis of Mooring Working Capacity ........................... 146

8-11 Mooring Line Tensions for a CVN-68 Moored at a Wharf with75 mph (33.5 m/s) Winds (Model 2) .............................................. 147

8-12 Aircraft Carrier Mooring Concept ....................................................... 1498-13 Wind Forces and Moments on a Nest of Four DD 963 Class

Vessels for a Wind Speed of 78 mph (35 m/s) ............................... 1518-14 Spread Mooring Arrangement for a Nest of Four Destroyers ............ 1538-15 End View of DD 963 Mooring Nest .................................................... 1568-16 Plate Anchor Holding Capacity .......................................................... 1608-17 LPD-17 USS SAN ANTONIO ............................................................ 1628-18 Approximate Safe Mooring Limits for LPD-17 with 28 Parts of

Mooring Line .................................................................................... 164

8-19 Sample LPD-17 Standard Mooring .................................................... 1668-20 Sample LPD-17 Storm Mooring ......................................................... 1678-21 Sample LPD-17 Heavy Weather Mooring .......................................... 1688-22 Sample LPD-17 Mooring at a Double-Deck Pier ............................... 169

9-1 Sample Passing Ship Situation .......................................................... 1729-2 Example of Passing Ship Predictions ................................................ 173

10-1 Ship Waves ..................................................................................... 17610-2 Ship Hull-Forms Tested ..................................................................... 17710-3 Maximum Wave Height One Wavelength Away From the Sailing

Line for a SERIES 60 Hull ................................................................. 178

11-1 Example of a Standard LPD 17 Mooring andHeavy Weather Mooring .................................................................... 182

11-2 Securing Two Parts of Heavy Weather Mooring Line ........................ 184

TABLESTable Title Page

2-1 Examples of Fixed Moorings.............................................................. 42-2 Examples of Fleet Moorings .............................................................. 8

3-1 Parameters in a Mooring Project ....................................................... 153-2 Basic Mooring Design Approach With Known Facility for a

Specific Site and a Specific Ship ..................................................... 163-3 Design Issues .................................................................................... 183-4 Mooring Service Types ...................................................................... 193-5 Facility Design Criteria for Mooring Service Types ............................ 213-6 Ship Mooring Hardware Design Criteria............................................. 22

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3-7 Minimum Quasi-Static Factors of Safety ........................................... 243-8 Recommended Practical Motion Criteria for Moored Vessels ........... 253-9 Quasi-Static Design Notes ................................................................. 283-10 Conditions Requiring Special Analysis .............................................. 30

3-11 Design Considerations Ship ........................................................... 363-12 Design Considerations Facility ........................................................ 373-13 Sample Distribution of Wind Gust Fronts on Guam (Agana NAS)

from 1982 to 1986 ........................................................................... 433-14 Storm Parameters .............................................................................. 463-15 Some Sources of Environmental Design Information ........................ 493-16 Mooring Operational Design Considerations ..................................... 503-17 Inspection Guidelines ........................................................................ 513-18 Design Recommendations ................................................................. 53

4-1 Engineering Properties of Air and Water ........................................... 55

4-2 Sample Wind Coefficients for Ships .................................................. 594-3 Recommended Ship Longitudinal Wind Force Drag Coefficients ...... 66

4-4 Recommended Values ofx ............................................................. 664-5 Normalized Wind Yaw Moment Variables ......................................... 704-6 Predicted Transverse Current Forces on FFG-7 for a Current Speed

of 1.5 m/s (2.9 knots) ...................................................................... 774-7 Area Ratio for Major Vessel Groups .................................................. 814-8 Example Destroyer ............................................................................ 824-9 Example Longitudinal Current Forces on a Destroyer ....................... 824-10 Current Moment Eccentricity Ratio Variables .................................... 84

5-1 Anchor Specification Considerations ................................................. 855-2 Anchor Characteristics ....................................................................... 895-3 Drag Anchor Holding Parameters U.S. Customary ............................ 925-4 Drag Anchor Holding Parameters SI Units ........................................ 935-5 Driven-Plate Anchor Components ..................................................... 965-6 Major Steps in Driven-Plate Anchor Installation ................................. 975-7 Typical Driven-Plate Anchors ............................................................. 98

6-1 Practical Experience With Anchors .................................................... 1006-2 Stockless Anchors in the U.S. Navy Fleet Mooring Inventory ............ 1016-3 NAVMOOR Anchors in the U.S. Navy Fleet Mooring Inventory ......... 102

6-4 FM3 Mooring Chain Characteristics ................................................... 1046-5 Properties of FM3 Chain Anodes ....................................................... 1056-6 Foam-Filled Polyurethane Coated Buoys .......................................... 1086-7 Stretch of Synthetic Lines .................................................................. 1096-8 Double Braided Nylon Line ................................................................ 1116-9 Double Braided Polyester Lines ........................................................ 1126-10 Some Factors to Consider When Specifying Synthetic Line or

Wire Rope ..................................................................................... 113

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6-11 Commonly Used U.S. Navy Pier Mooring Fittings ............................. 1176-12 Sources of Information for Facility Mooring Equipment ..................... 122

7-1 Types of Ship Based Mooring Equipment ......................................... 125

7-2 Fixed Ships Bitts (minimum strength requirements) ........................ 1277-3 Closed Chocks (minimum strength requirements) ............................ 1297-4 Sources of Information for Ships Mooring Equipment ...................... 130

8-1 2nd LT JOHN P BOBO Parameters (Fully Loaded) .......................... 1338-2 CVN-68 Criteria (Fully Loaded) ......................................................... 1378-3 DD 963 Criteria (1/3 Stores) ............................................................. 1508-4 Environmental Forces ........................................................................ 1508-5 Quasi-Static Leg Tensions for the Spread Mooring at Various

Wind Directions With a Flood Tidal Current .................................... 1548-6 Peak Dynamic Chain Tensions for DD 963 Nest for Various Wind

Directions and a Flood Tidal Current ............................................... 1578-7 DD 963 Nest Motions for Surge, Sway, and Yaw at Various Wind

Directions With a Flood Tidal Current .............................................. 1588-8 LPD-17 Characteristics ...................................................................... 163

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CHAPTER 1

INTRODUCTION

1-1 PURPOSE AND SCOPE. This UFC provides design policy andprocedures for design of moorings for U.S. Department of Defense (DOD) vessels.

1-2 PURPOSE OF CRITERIA. The purpose of this UFC is to ensure quality,consistency, and safety of DOD vessels, mooring hardware, and mooring facilitiesthroughout the world. Other criteria should not be used without specific authorization.

1-3 DEFINITION. A mooring, in general terms, is defined as a compliantstructure that restrains a vessel against the action of wind, wave, and current forces.For the purposes of this UFC, the emphasis is on moorings composed of tensionmembers (chain, line, wire rope, etc.) and compression members (fenders, camels,

etc.) used to secure vessels (surface ships, submarines, floating drydocks, yard craft,etc.). The term mooring in this UFC includes anchoring of ships.

1-4 CANCELLATION. This UFC cancels and supersedes MIL-HDBK-1026/4Mooring Design, Naval Facilities Engineering Command, July 1999.

1-5 ORGANIZATIONAL ROLES AND RESPONSIBILITIES. Over the designlife of a mooring facility, many organizations are involved with the various aspects of afacility. Personnel involved range from policy makers, who set the initial missionrequirements for vessels and facilities, to deck personnel securing lines. Figure 1illustrates the DOD organizations that must understand the various aspects of

moorings. In addition, all these groups must maintain open communications to ensuresafe and effective moorings.

Safe use of moorings is of particular importance for the end users (the ship's personneland facility operators). They must understand the safe limits of a mooring to properlyrespond to significant events, such as a sudden storm, and to be able to meet missionrequirements.

It is equally important for all organizations and personnel shown in Figure 1-1 tounderstand moorings. For example, if the customer setting the overall missionrequirement states "We need a ship class and associated facilities to meet mission X,

and specification Y will be used to obtain these assets" and there is a mismatchbetween X and Y, the ship and facility operators can be faced with a lifetime ofproblems, mishaps, and/or serious accidents.

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Figure 1-1. DOD Organizations Involved With Ship Moor ings

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CHAPTER 2

MOORING SYSTEMS

2-1 INTRODUCTION. The DOD uses several types of mooring systems tomoor ships. These systems can be summarized into two broad categories of moorings:

a) Fixed Moorings - Fixed moorings are defined as systems that includetension and compression members. Typical fixed mooring systemsinclude moorings at piers and wharves.

b) Fleet Moorings - Fleet moorings are defined as systems that includeprimarily tension members. Mooring loads are transferred into the earthvia anchors. Examples of fleet moorings include fleet mooring buoys andships anchor systems.

The more common types of moorings are discussed in this chapter.

2-1.1 PURPOSE OF MOORING. The purpose of a mooring is to safely hold aship in a certain position to accomplish a specific mission. A key need is to safely holdthe vessel to protect the ship, life, the public interest, and to preserve the capabilities ofthe vessel and surrounding facilities. Ship moorings are provided for:

a) Loading/Unloading - Loading and unloading items such as stores,cargo, fuel, personnel, ammunition, etc.

b) Ship Storage - Storing the ship in a mooring reduces fuel consumptionand personnel costs. Ships in an inactive or reserve status are stored atmoorings.

c) Maintenance/Repairs - Making a variety of repairs or conductingmaintenance on the ship is often performed with a ship moored.

d) Mission - Moorings are used to support special mission requirements,such as surveillance, tracking, training, etc.

Most DOD moorings are provided in harbors to reduce exposure to waves, reduce ship

motions, and reduce dynamic mooring loads. Mooring in harbors also allows improvedaccess to various services and other forms of transportation.

2-2 TYPES OF MOORING SYSTEMS. Examples of typical mooringssystems are given in this chapter.

2-2.1 Fixed Mooring Systems. Examples of typical fixed moorings are given inTable 2-1 and illustrated in Figures 2-1 through 2-5.

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2-2.2 Fleet Mooring Systems. Examples of typical fleet moorings are given inTable 2-2 and illustrated in Figures 2-6 through 2-13.

Table 2-1. Examples of Fixed Moorings

a. Single Vessel Secured at Multiple Points

MOORING TYPE FIGURENUMBER

DESCRIPTION

Pier/Wharf 2-12-2

Multiple tension lines are used to secure a vesselnext to a pier/wharf. Compliant fenders, fenderpiles and/or camels keep the vessel offset fromthe structure. A T-pier may be used to keep theship parallel to the current, where the currentspeed is high.

Spud Mooring 2-3 Multiple vertical structural steel beams are used tosecure the vessel, such as a floating drydock.This type of mooring is especially effective forconstruction barges temporarily working in shallowwater. Spud moorings can be especiallysusceptible to dynamic processes, such as harborseiches and earthquakes.

b. Multiple Vessel Moorings

MOORING TYPE FIGURE

NUMBER

DESCRIPTION

Opposite Sides of a Pier 2-4 Vessels can be placed adjacent to one another onopposite sides of a pier to provide some blockageof the environmental forces/moments on thedownstream vessel.

Multiple Vessels Next toOne Another

2-5 Vessels can be placed adjacent to one another toprovide significant blockage of the environmentalforces/ moments on the downstream vessel(s).

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Figure 2-1. Single Ship, Offset From a Pier With Camels

Figure 2-2. Ship at a T-Pier (plan view)

CURRENT

MOORING

CAMELS

STORM BOLLARDS

LPD-17

LINE

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Figure 2-3. Floating Drydock Spud Moored (spuds are secured to a pier, which isnot shown, and the floating drydock rides up and down on the spuds; profile viewis shown)

Figure 2-4. Ships on Both Sides of a Pier (plan view)

LINESCAMELS

PIER

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Figure 2-5. Two Ships on One Side of a Pier (plan view)

Table 2-2. Examples of Fleet Moorings

a. Vessel Secured at a Single Point

MOORING TYPE FIGURENUMBER DESCRIPTION

At Anchor 2-6 Typical configuration includes the ship deploying asingle drag anchor off the bow. This is usually atemporary mooring used as a last resort in benignconditions. A large amount of harbor room isrequired for the ship swing watch circle. If thewind changes direction dramatically then theanchor will have to reset. Dynamic fishtailing,even under steady winds and currents, may be aproblem. Putting out a second anchor in what isknown as a Hammerlock mooring may berequired in storm anchoring.

Single Mooring Buoy 2-72-8

A single point mooring (SPM) buoy is secured tothe seafloor typically with 1 to 12 ground legs andeither drag or plate anchors. The ship moors tothe buoy using an anchor chain or hawser. Thevessel weathervanes under the action of forcing,which helps to reduce the mooring load. This typeof mooring requires much less room than a ship atanchor because the pivot point is much closer tothe vessel. A vessel at a mooring buoy is muchless prone to fishtailing than a ship at anchor.Many of the mooring buoys at U.S. Navy facilitiesaround the world are provided under the U.S.Navys Fleet Mooring Program.

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Table 2-2. (continued) Examples of Fleet Moorings

b. Vessel Secured at Two Points


Bow-Stern Mooring 2-9 A vessel is moored with one buoy to the bow andanother to the stern. This system has a muchsmaller watch circle than a vessel at a singlemooring buoy. Also, two moorings share the load.However, the mooring tension can be much

higher if the winds, currents, or waves have alarge broadside component to the ship.

c. Vessel Secured at Multiple Points


Med-Mooring 2-10 The vessel bow is secured to two mooring buoysand the stern is moored to the end of a pier orwharf. This type of mooring is commonly used fortenders or in cases where available harbor spaceis limited. Commonly used in the MediterraneanSea. Hence, the term Med Mooring.

Spread Mooring 2-11 Multiple mooring legs are used to secure a vessel.This arrangement of moorings is especially useful

for securing permanently or semi-permanently

moored vessels, such as floating drydocks andinactive ships. The ship(s) are usually orientedparallel to the current.

d. Multiple Vessel Moorings

MOORING TYPE FIGURENUMBER

DESCRIPTION

Nest2-122-13

Multiple tension members are used to secureseveral vessels together. Separators are used tokeep the vessels from contacting one another.Nests of vessels are commonly put into spread

moorings. Nested vessels may be of similar size(as for inactive ships) or much different size (as asubmarine alongside a tender). Advantages ofnesting are: a nest takes up relatively little harborspace and forces/moments on a nest may be lessthan if the ships were moored individually.

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Figure 2-6. Ship at Anchor

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Figure 2-7. Single Point Mooring With Drag Anchors

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Figure 2-8. Single Point Mooring With a Plate Anchor and a Sinker

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Figure 2-10. Med-Mooring

Figure 2-9. Bow-Stern Mooring Shown in Plan View

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Figure 2-11. Spread Mooring

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Figure 2-12. Two inactive ships moored at a wharf (separators between ships not

shown)

Figure 2-13. Spread Mooring

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CHAPTER 3

BASIC DESIGN PROCEDURE

3-1 DESIGN APPROACH. Begin the design with specified parameters anduse engineering principles to complete the design. Types of parameters associated withmooring projects are summarized in Table 3-1. The basic approach to performingmooring design with the facility and ship known is given in Table 3-2.

Table 3-1. Parameters in a Mooring Project

PARAMETER EXAMPLES

1. Operational Parameters Required ship position, amount of

motion allowed2. Ship Configuration Basic ship parameters, such as length,width, draft, displacement, wind areas,mooring fitting locations, wind/currentforce, and moment coefficients

3. Facility Configuration Facility location, water depth,dimensions, locations/type/capacity ofmooring fittings/fenders, facilitycondition, facility overall capacity

4. Environmental Parameters Wind speed, current speed anddirection, water levels, wave conditions

and possibility of ice5. Mooring Configuration Number/size/type/location of tensionmembers, fenders, camels, etc.

6. Material Properties Stretch/strain characteristics of themooring tension and compressionmembers

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Table 3-2. Basic Mooring Design Approach With Known Facility fora Specific Site and a Specific Ship

STEP NOTES

Define customer(s)requirements

Define the ship(s) to be moored, the type of servicerequired, the maximum allowable ship motions, andsituations under which the ship will leave.

Determine planningrequirements

Define the impact/interaction with other facilitiesand operations, evaluate explosive arcs, determinepermit requirements, establish how the mooring isto be used, review the budget and schedule.

Environmental ImpactAssessments

Prepare any required studies and paperwork.

Define site and

environmentalparameters

Determine the water depth(s), engineering soil

parameters, design winds, design currents, designwaves, design water levels, and evaluate access.

Ship characteristics Find the characteristics of the ship(s) including sailareas, drafts, displacements, ship mooring fittings,allowable hull pressures, and other parameters.

Ship forces/moments Determine the forces, moments, and other keybehaviors of the ship(s).

Evaluate mooringalternatives

Evaluate the alternatives in terms of safety, risk,cost, constructability, availability of hardware,impact on the site, watch circle, compatibility,maintenance, inspectability, and other important

aspects.Design Calculations Perform static and/or dynamic analyses (if required)for mooring performance, anchor design, fenderdesign, etc

Notifications Prepare Notice to Mariners for the case of in-waterconstruction work and notify charting authoritiesconcerning updating charts for the area.

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Table 3-2. (continued) Basic Mooring Design Approach With Known Facility fora Specific Site and a Specific Ship

STEP NOTE

Plans/Specs Prepare plans, specifications, and cost estimates.

Permits Prepare any required environmental studies andobtain required permits.

Installation planning Prepare instructions for installation, including safetyand environmental protection plans.

Installation monitoring Perform engineering monitoring of the installationprocess.

Testing Perform pull tests of all anchors in mooring facilitiesto ensure that they hold the required load.

Documentation Document the design and as-built conditions with

drawings and reports.Instructions Provide diagrams and instructions to show thecustomer how to use and inspect the mooring.

Inspection Perform periodic inspection/testing of the mooringto assure it continues to meet the customer(s)requirements.

Maintenance Perform maintenance as required and document onas-built drawings.

3-2 GENERAL DESIGN CRITERIA. General design issues shown in Table 3-

3 should be addressed during design to help ensure projects meet customers needs.

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Table 3-3. Design Issues

CRITERIA NOTES

Vessel operatingconditions Under what conditions will the vessel(s) exit? What are theoperating mission requirements for the ship? What is themaximum allowable hull pressure?

Allowable motions How much ship motion in the six degrees-of-freedom will beallowable for the moored ship? This is related to browpositions and use, utilities, ship loading and unloadingoperations, and other requirements. Note that most shipshave a very high buoyancy force and moorings should bedesigned to allow for water level changes at a site.

User skills Is the user trained and experienced in using the proposedsystem? What is the risk that the mooring would be

improperly used? Can a design be formulated for easy andreliable use?

Flexibility How flexible is the design? Can it provide for new missionrequirements not yet envisioned? Can it be used withexisting facilities/ships?

Constructability Does the design specify readily available commercialproducts and is it able to be installed and/or constructedusing standard techniques, tolerances, etc.?

Cost Are initial and life cycle costs minimized?

Inspection Can the mooring system be readily inspected to ensurecontinued good working condition?

Maintenance Can the system be maintained in a cost-effective manner?Special requirements What special requirements does the customer have? Are

there any portions of the ship that cannot come in contactwith mooring elements (e.g., submarine hulls)?

3-2.1 Mooring Service Types. Four Mooring Service Types are defined to helpidentify minimum design requirements associated with DoD ships and piers, anddetermine operational limitations. Facility and ship mooring hardware shouldaccommodate the service types shown in Table 3-4.

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Table 3-4. Mooring Service Types

MOORING SERVICETYPE

DESCRIPTION

TYPE IMild Weather Mooring

This category covers moorings for mild weather(sustained winds of less than 35 knots; below gale force)and currents less than 1 knot. Mooring situations includeammunition facilities, fueling facilities, depermingfacilities, and ports of call. Use of these moorings isnormally selected in concert with forecasted weather.

TYPE II

TYPE IIA StandardMooring

TYPE IIB StormMooring

This category covers moorings that are used throughstorm conditions. Moorings include standard, storm andnested configurations. Vessel will normally leave prior toan approaching hurricane, typhoon, surge or otherextreme event. Naval ships intend to go to sea if 50 knotwinds are expected, but storms may come up quickly, sohigher design winds are recommended.MST IIA covers mooring in winds of 50 knots or less inbroadside currents of 1-1/2 knots or less. The practice isto provide for full pier operation for MST IIA.MST IIB covers mooring in winds of 64 knot or less inbroadside currents of a 2 knots or less. This is theintended Navy ship mooring design requirement. It isencouraged for general home porting because suddenstorms can produce high winds on short notice. Pieroperations may be impacted for MST IIB if lines must berun across a pier.

TYPE IIIHeavy WeatherMooring

This category covers moorings of vessels that cannot ormay not get underway prior to an approaching hurricaneor typhoon. Moorings include fitting-out, repair,drydocking, and overhaul berthing facilities.

TYPE IVPermanent Mooring

This category covers moorings that are used topermanently moor a vessel that will not leave in case ofa hurricane, typhoon, or surge. Moorings includeinactive ships, floating drydocks, ship museums, trainingberthing facilities, etc.

3-2.2 Facili ty Design Criteria for Mooring Service Types. Mooring facilitiesare designed conforming to the site specific environmental criteria given in Table 3-5.Table 3-5 gives design criteria in terms of environmental design return intervals, R, andin terms of probability of exceedence, P, for 1 year of service life, N=1. The shipusually has the responsibility for providing mooring lines for Mooring Service Types Iand II, while the facility usually provides mooring lines for Mooring Service Types III andIV.

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3-2.3 Ship Hardware Design Criteria for Mooring Service Types. Shipmooring hardware needs to be designed to accommodate various modes of shipoperation. During Type II operation, a ship may be moored in relatively high broadsidecurrent and get caught by a sudden storm, such as a thunderstorm. Type III mooring

during repair may provide the greatest potential of risk, because the ship is moored fora significant time and cannot get underway. There are several U.S. shipyards whereDOD ships can undergo major repairs. The area near Norfolk/Portsmouth, VA hassome of the most extreme design criteria, so ships hardware design should be basedon conditions derived from this site. Ship mooring hardware environmental designcriteria are given in Table 3-6. During Type IV mooring, the ship is usually aligned withthe current, extra padeyes can be welded to the ship hull for mooring, etc., so specialprovisions can be made for long-term storage.

3-2.4 Strength. Moorings should be designed and constructed to safely resistthe nominal loads in load combinations defined herein without exceeding the

appropriate allowable stresses for the mooring components. Normal wear of materialsand inspection methods and frequency need to be considered. Due to the probability ofsimultaneous maximum occurrences of variable loads, no reduction factors should beused.

3-2.5 Serviceability. Moorings should be designed to have adequate stiffnessto limit deflections, vibration, or any other deformations that adversely affect theintended use and performance of the mooring. At the same time moorings need to beflexible enough to provide for load sharing, reduce peak dynamic loads and allow forevents, such as tidal changes.

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Table 3-5. Facili ty Design Criteria for Mooring Service Types

MOORING

SERVICE TYPE

\1\ WIND/1/ \1\CURRENT

2 /1/

WATER

LEVEL

WAVES

TYPE I \1\Less than 35 knots/1/

1 knot or less mean lowerlow to meanhigher high

N.A.

TYPE IIA Vw=50 knots (max.) 1.5-knot max. extreme low tomean higherhigh

P=1 orR=1 yr

TYPE IIB Vw=64 knots (max.) 2.0-knot max. extreme low tomean higherhigh

P=1 orR=1 yr

TYPE III P=0.02 orR=50 yr P=0.02 orR=50 yr extreme low tomean higherhigh

P=0.02 orR=50 yr

\1\ TYPE IV /1/ P=0.01 orR=100 yr

P=0.01 orR=100 yr

extreme waterlevels

P=0.01 orR=100 yr

\1\

1Use exposure D (UFC 1-200-01 General Building Requirements; flat, unobstructed

area exposed to wind flowing over open water for a distance of at least 1 mile or 1.61km) for determining design wind speeds. Note that min. = minimum return interval or

probability of exceedence used for design; max. = maximum wind speed used fordesign.

2To define the design water depth for ship mooring systems, use T/d=0.9 for flat keeled

ships; for ships with non-flat hulls, that have sonar domes or other projections, take theship draft, T, as the mean depth of the keel and determine the water depth, d, byadding 0.61 meter (2 feet) to the maximum navigation draft of the ship (note, may varydepending on sonar dome size)

3This is considered an absolute minimum for design. Specific site conditions might

dictate consideration of a higher windspeed. Local wind climatology should be

examined to determine appropriate windspeed.4Refer to SSR-NAVFAC ESC-06-2012 Environmental Conditions Reportfor obtaining

wind, current, and water level for recurrence intervals associated with Type III and TypeIV mooring service types.

/1/

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Table 3-6. Ship Mooring Hardware Design Criteria

a. Ship Anchor Systems*

VESSEL TYPE MINIMUM

WATERDEPTH

MINIMUM

WINDSPEED

MINIMUM

CURRENTSPEED

Ships 240 ft73 m

70 knots32.9 m/s

4 knots1.54 m/s

Submarines 120 ft36.6 m

70 knots36.0 m/s

4 knots2.06 m/s

b. Ship Mooring Systems**

MOORING SERVICE TYPE MINIMUM WIND SPEED MINIMUMCURRENTSPEED

Type I 35 knots18.0 m/s

1 knot0.51 m/s

Type II*** 64 knots33.0 m/s

2 knots1.03 m/s

Type III 95 knots48.9 m/s

2 knots1.03 m/s

*Quasi-static design assuming wind and current are co-linear for ship and submarineanchor systems (after NAVSEASYSCOM DDS-581).

**To define the design water depth, use T/d=0.9 for flat keeled ships; for ships with non-flat hulls, that have sonar domes or other projections, take the ship draft, T, as themean depth of the keel and determine the water depth, d, by adding 0.61 meter (2 feet)to the maximum navigation draft of the ship (note, may vary depending on sonar domesize).

***Ships need to carry lines suitable for MST IIB.

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3-2.6 Design Methods. All moorings should be designed byskilled/knowledgeable professional personnel. Methods must be used that assure thatships are safely moored. Below are some guidelines.

Mooring Service Type I and II moorings can often be designed using quasi-static toolswith 3 degrees-of-freedom (surge, sway and yaw). Examples of tools includeFIXMOOR (Note: \1\ FIXMOOR is available at:http://www.wbdg.org/tools/fixmoor.php?u=7 /1/ ), OPTIMOOR, AQWA LIBRIUM, etc.Specialized tools need to be considered for cases of high currents, high tidal ranges,passing ship effects, ship waves, multiple/nested ships, situations that are likely to bedynamic and other specialized cases. It is valuable to ships and port operationspersonnel to provide generalized mooring designs for Mooring Service Types I and II.

Mooring Service Types III and IV must be designed on a case-by-case basis usingdynamic methods because of the extremely high loading that occurs during extreme

storms. It is recommended that NFESC be contacted concerning the design of thesetypes of moorings.

3-2.7 General Mooring Integrity. For multiple-member moorings, such as for aship secured to a pier by a number of lines, the mooring system strongly relies on loadsharing among several members. If one member is lost, the ship should remainmoored. Therefore, design multiple member mooring to ensure that remainingmembers maintain a factor of safety at least 75 percent of the intact mooring factors ofsafety shown in Table 3-7 with any one member missing.

3-2.8 Quasi-Static Safety Factors. Table 3-7 gives recommended minimum

factors of safety for quasi-static design based on material reliability.

3-2.9 Allowable Ship Motions. Table 3-8 gives recommended operational shipmotion criteria for moored vessels. Table 3-8(a) gives maximum wave conditions formanned and moored small craft (Permanent International Association of NavigationCongresses (PIANC), Criteria for Movements of Moored Ships in Harbors; A PracticalGuide, 1995). These criteria are based on comfort of personnel on board a small boat,and are given as a function of boat length and locally generated.

Table 3-8(b) gives recommended motion criteria for safe working conditions for varioustypes of vessels (PIANC, 1995).

Table 3-8(c) gives recommended velocity criteria and Table 3-8(d) and (e) give specialcriteria.
http://www.wbdg.org/tools/fixmoor.php?u=7http://www.wbdg.org/tools/fixmoor.php?u=7http://www.wbdg.org/tools/fixmoor.php?u=7

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Table 3-7. Minimum Quasi-Static Factors of SafetyCOMPONENT MINIMUM

FACTOR OFSAFETY

NOTES

Stockless & balancedfluke anchors

1.5 For ultimate anchoring system holding capacity;use 1.0 for ship's anchoring*

High efficiency draganchors

2.0 For ultimate anchoring system holding capacityuse 1.0 for ship's anchoring*

Fixed anchors (piles &plates)

3.0 For ultimate anchoring system holding capacity*

Deadweight anchors - Use carefully (see Naval Civil EngineeringLaboratory (NCEL) Handbook for MarineGeotechnical Engineering, 1985)

Chain

3.0

4.0

For relatively straight lengths.

For chain around bends.These factors of safety are for the new chainbreak strength.

Wire rope 3.0 For the new wire rope break strength.

Synthetic line** 3.0 For new line break strength.

Ship bitts *** Use American Institute of Steel Construction(AISC) code.

Pier bollards *** Use AISC & other applicable codes.

*It is recommended that anchors be pull tested.**Reduce effective strength of wet nylon line by 15 percent.

*** For mooring fittings take 3 parts of the largest size of line used on the fitting; apply aload of: 3.0*(minimum line break strength)*1.3 to determine actual stresses, act.;design fittings so (act./ allow.)

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Table 3-8. Recommended Practical Motion Criteria for Moored Vessels

(a) Safe Wave Height Limits for Moored Manned Small Craft(after PIANC, 1995)

Beam/Quartering Seas Head Seas

VesselLength (m)

WavePeriod (sec)

MaximumSign WaveHeight, Hs(m)

WavePeriod (sec)

MaximumSign WaveHeight, Hs(m)

4 to 10 4.0 0.20

10-16 5.5 0.30

20 7.0 0.30

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Table 3-8. (continued) Recommended Practical Motion Criteria for MooredVessels

(b) Recommended Motion Criteria for Safe Working Conditions1

(after PIANC, 1995)

VesselType

Cargo HandlingEquipment

Surge(m)

Sway(m)

Heave(m)

Yaw(o)

Pitch(o)

Roll(o)

Fishingvessels10-3000GRT

2

Elevator craneLift-on/offSuction pump

0.151.02.0

0.151.01.0

-0.4-

-3-

-3-

-3-

Freighters&coasters

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Table 3-8. (continued) Recommended Practical Motion Criteria for MooredVessels

(c) Recommended Velocity Criteria for Safe Mooring Conditions for Fishing Vessels,Coasters, Freighters, Ferries and Ro/Ro Vessels (after PIANC, 1995)

ShipSize(DWT)

Surge(m/s)

Sway(m/s)

Heave(m/s)

Yaw(o/s)

Pitch(o/s)

Roll(o/s)

1000 0.6 0.6 - 2.0 - 2.0

2000 0.4 0.4 - 1.5 - 1.5

8000 0.3 0.3 - 1.0 - 1.0

(d) Special Criteria for Walkways and Rail Ramps

(after PIANC, 1995)

Parameter Maximum Value

Vertical velocity 0.2 m/s

Vertical acceleration 0.5 m/s

(e) Special Criteria

CONDITION MAXIMUMAMPLITUDEVALUES

NOTES

Heave - Ships will move vertically with anylong period water level change (tide,storm surge, flood, etc.). Theresulting buoyancy forces may behigh, so the mooring must bedesigned to provide for these motionsdue to long period water levelchanges.

Loading/unloading

preposition ships

0.6 m (2

feet)

Maximum ramp motion during

loading/unloading moving wheeledvehicles.

Weaponsloading/unloading

0.6 m (2feet)

Maximum motion between the craneand the object beingloaded/unloaded.

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3-3 DESIGN METHODS

3-3.1 Quasi-Static Design. Practical experience has shown that in manysituations such as for Mooring Service Types I and II, static analysis tools, such as

FIXMOOR \1\/1/, OPTIMOOR and AQWA LIBRIUM, can be used to reliably determinemooring designs in harbors. Winds are a key forcing factor in mooring harbors. Windscan be highly dynamic in heavy weather conditions. However, practical experience hasshown that for typical DOD ships, a wind speed with a duration of 30 seconds can beused, together with static tools, to develop safe mooring designs. The use of the 30-second duration wind speed with static tools and the approach shown in Table 3-9 iscalled quasi-static design.

Table 3-9. Quasi-Static Design Notes

CRITERIA NOTES

Wind speed Determine for the selected return interval, R. Fortypical ships use the wind that has a duration of30 seconds at an elevation of 10 m.

Wind direction Assume the wind can come from any directionexcept in cases where wind data show extremewinds occur in a window of directions.

Current speed Use conditions for the site (speed and direction).

Water levels Use the range for the site.

Waves Neglected. If waves are believed to beimportant, then dynamic analyses are

recommended.Factors of safety Perform the design using quasi-static forces andmoments (see Chapter 4), minimum factors ofsafety in Table 3-7, and design to assure that allcriteria are met.

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3-3.2 Dynamic Mooring Analysis. Conditions during Mooring Service Types IIIand IV, and during extreme events can be highly dynamic. Unfortunately, the dynamicbehavior of a moored ship in shallow water can be highly complex, so dynamics cannotbe fully documented in this UFC. An introduction to dynamics is provided in Chapter 8.

Information on dynamics is found in: Dynamic Analysis of Moored Floating Drydocks,Headland et. al. (1989); Advanced Dynamics of Marine Structures, Hooft (1982);Hydrodynamic Analysis and Computer Simulation Applied to Ship Interaction DuringManeuvering in Shallow Channels, Kizakkevariath (1989); David Taylor ResearchCenter (DTRC), SPD-0936-01, Users Manual for the Standard Ship Motion Program,SMP81; Low Frequency Second Order Wave Exciting Forces on Floating Structures,Pinkster (1982); Mooring Dynamics Due to Wind Gust Fronts, Seelig and Headland(1998); and A Simulation Model for a Single Point Moored Tanker, Wichers (1988).Some conditions when mooring dynamics may be important to design or whenspecialized considerations need to be made are given in Table 3-10.

The programs AQWA DRIFT and AQWA NAUT (Century Dynamics, Houston, TX) areexamples of software tools that can be used to simulate highly dynamic mooringsituations.

3-4 RISK. Risk is a concept that is often used to design facilities, because theprobability of occurrence of extreme events (currents, waves, tides, storm surge,earthquakes, etc.) is strongly site dependent. Risk is used to ensure that systems arereliable, practical, and economical.

A common way to describe risk is the concept of return interval, which is the meanlength of time between events. For example, if the wind speed with a return interval of

R = 100 years is given for a site, this wind speed would be expected to occur, on theaverage, once every 100 years. However, since wind speeds are probabilistic, thespecified 100-year wind speed might not occur at all in any 100-year period. Or, in any100-year period the wind speed may be equal to or exceed the specified wind speedmultiple times.

The probability or risk that an event will be equaled or exceeded one or more timesduring any given interval is determined from:

EQUATION: P = 100%*(1-(1-1/R) )N (1)

where

P = probability, in percent, of an event

being equaled or exceeded one or moretimes in a specified interval

R = return interval (years)N = service life (years)

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Figure 3-1 shows risk versus years on station for various selected values of returninterval. For example, take a ship that is on station at a site for 20 years (N = 20).There is a P = 18.2 percent probability that an event with a return interval of R = 100years or greater will occur one or more times at a site in a 20-year interval.

Table 3-10. Conditions Requir ing Special Analysis

FACTOR SPECIAL ANALYSIS REQUIRED

Wind > 45 mph for small craft> 75 mph for larger vessels

Wind waves > 1.5 ft for small craft> 4 ft for larger vessels

Wind gust fronts Yes for SPMs

Current > 3 knots

Ship waves and passing ship effects Yes for special cases (seeKizakkevariath, 1989; Occasion,1996; Weggel and Sorensen, 1984 &1986)

Long waves (seiches and tidal waves ortsunamis)

Yes

Berthing and using mooring as a break Yes (see \1\ UFC 4-152-01, Design:Piers and Wharves /1/)

Parting tension member May be static or dynamic

Ship impact or other sudden force on theship

Yes (if directed)

Earthquakes (spud moored or stiffsystems)

Yes

Explosion, landslide, impact Yes (if directed)

Tornado (reference NUREG 1974) Yes

Flood, sudden water level rise Yes (if directed)

Ice forcing Yes (if a factor)

Ship/mooring system dynamicallyunstable (e.g., SPM)

Yes (dynamic behavior of ships atSPMs can be especially complex)

Forcing period near a natural period of themooring system

Yes; if the forcing period is from 80%to 120% of a system natural period

Note: SPM = single point mooring

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Figure 3-1. Risk Diagram

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3-5 COORDINATE SYSTEMS. The various coordinate systems used forships and mooring design are described below.

3-5.1 Ship Design/Construction Coordinates. A forward perpendicular point

(FP), aft perpendicular point (AP), and regular spaced frames along the longitudinalaxes of the ship are used to define stations. The bottom of the ship keel is usually usedas the reference point or baseline for vertical distances. Figure 3-2 illustrates shipdesign coordinates.

3-5.2 Ship Hydrostatics/Hydrodynamics Coordinates. The forwardperpendicular is taken as Station 0, the aft perpendicular is taken as Station 20, andvarious cross-sections of the ship hull (perpendicular to the longitudinal axis of the ship)are used to describe the shape of the ship hull. Figure 3-2 illustrates ship hydrostaticconventions.

3-5.3 Local Mooring Coordinate System. Environmental forces on ships area function of angle relative to the vessels longitudinal centerline. Also, a ship tends tomove about its center of gravity. Therefore, the local right-hand-rule coordinatesystem, shown in Figure 3-3, is used in this UFC. The midships point is shown as aconvenient reference point in Figures 3-3 and 3-4.

3-5.4 Global Coordinate System. Plane state grids or other systems are oftenused to describe x and y coordinates. The vertical datum is most often taken asrelative to some water level, such as mean lower low water (MLLW).

3-5.5 Ship Conditions. Loading conditions are defined in NAVSEA

NSTM 096. There are three common conditions or displacements that a ship has atvarious stages including:

Light Condition This is the ship condition after first launching.

One-Third Stores Condition This is the typical ship condition during shiprepair, as indicated in SUPSHIP docking/undocking records.

Fully Loaded Condition This is the ship condition during operations.

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Figure 3-2. Ship Design and Hydrostatic Coordinates

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Figure 3-3. Local Mooring Coordinate System for a Ship

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Figure 3-4. Local Mooring Coordinate System for a Ship

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3-6 VESSEL DESIGN CONSIDERATIONS. Some important vessel mooringdesign considerations are summarized in Table 3-11. General information on ships canbe found in the Ships Characteristics Database \1\(http://www.wbdg.org/tools/ships.php?u=7)/1/and in the NAVSEA Hitchhikers Guide to

Navy Surface Ships.

Table 3-11. Design Considerations - Ship

PARAMETER NOTES

Ship fittings The type, capacity, location, and number ofmooring fittings on the ship are critical in designingmoorings.

Ship hardware The type, capacity, location, and number of othermooring hardware (chain, anchors, winches, etc.)

on the ship are critical.Buoyancy The ships buoyancy supports the ship up in theheave, pitch, and roll directions. Therefore, it isusually undesirable to have much mooring capacityin these directions. A large ship, for example, mayhave over a million pounds of buoyancy for a footof water level rise. If an unusually large water levelrise occurs for a mooring with a large component ofthe mooring force in the vertical direction, this couldresult in mooring failure.

Hull pressures Ships are designed so that only a certain allowable

pressure can be safely resisted. Allowable hullpressures and fender design are discussed inNFESC TR-6015-OCN, Foam-Filled Fender Designto Prevent Hull Damage.

Personnel access Personnel access must be provided.

Cargo Loading Ramps/sideport locations

Hotel services Provision must be made for utilities and other hotelservices.

Ship condition Ships are typically in the Light, One-Third Storesor Fully-Loaded condition or displacement.

3-7 FACILITY DESIGN CONSIDERATIONS. Some important facility mooringdesign considerations are summarized in Table 3-12.

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Table 3-12. Design Considerations - Faci lity

PARAMETER NOTES

Access Adequate ship access in terms of channels,turning basins, bridge clearance, etc. needsto be provided. Also, tugs and pilots must beavailable.

Mooring fittings The number, type, location and capacity ofmooring fittings or attachment point have tomeet the needs of all vessels using thefacility.

Fenders The number, type, location, and propertiesof marine fenders must be specified to

protect the ship(s) and facility.Water depth The water depth at the mooring site must beadequate to meet the customers needs.

Shoaling Many harbor sites experience shoaling. Theshoaling and possible need for dredgingneeds to be considered.

Permits Permits (Federal, state, environmental,historical, etc.) are often required for facilitiesand they need to be considered.

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3-8 ENVIRONMENTAL FORCING DESIGN CONSIDERATIONS.Environmental forces acting on a moored ship(s) can be complex. Winds, currents,water levels, and waves are especially important for many designs. \1\ /1/

3-8.1 Winds. A change in pressure from one point on the earth to anothercauses the wind to blow. Turbulence is carried along with the overall wind flow toproduce wind gusts. If the mean wind speed and direction do not change very rapidlywith time, the winds are referred to as stationary.

Practical experience has shown that wind gusts with a duration of approximately 30seconds or longer have a significant influence on typical moored ships withdisplacements of about 1000 tons or larger. Vessels with shorter natural periods canrespond to shorter duration gusts. For the purposes of this UFC, a 30-second windduration at a 10-meter (33-foot) elevation is recommended for the design forstationary winds. The relationship of the 30-second wind to other wind durations is

shown in Figure 3-5.

If wind speed and/or direction changes rapidly, such as in a wind gust front, hurricaneor tornado, then winds are non-stationary. Figure 3-6, for example, shows a recordingfrom typhoon OMAR in 1992 at Guam. The eye of this storm went over the recordingsite. The upper portion of this figure shows the wind speed and the lower portion of thefigure is the wind direction. Time on the chart recorder proceeds from right to left. Thishurricane had rapid changes in wind speed and direction. As the eye passes there isalso a large-scale change in wind speed and direction.

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0.70

0.75

0.80

0.85

0.90

0.95

1.00

1.05

1.10

1.15

1.20

1.25

1.30

1 10 100 1000 10000

GUST DURATION, t (sec)

Vt/V30

NON-HURRICANE

HURRICANE

Figure 3-5. Ratio of Wind Speeds for Various Gusts (after ASCE 7-95)

t Vt/V30 Vt/V30

(sec) N on-Hurricane H urric ane

1 1.182 1.221

2 1.160 1.196

3 1.145 1.175

5 1.124 1.147

10 1.080 1.097

20 1.030 1.034

30 1.000 1.00040 0.977 0.971

50 0.955 0.950

60 0.938 0.932

70 0.924 0.917

100 0.891 0.879

200 0.846 0.822

400 0.815 0.780

1000 0.783 0.739

3600 0.753 0.706

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WIND SPEED

EYE

TIME1 hour

WIND DIRECTION

Figure 3-6. Typhoon OMAR Wind Chart Recording

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3-8.2 Wind Gust Fronts . A particularly dangerous wind condition that hascaused a number of mooring accidents is the wind gust front (Mooring Dynamics Due toWind Gust Fronts, Seelig and Headland, 1998 and CHESNAVFACENGCOM, FPO-1-87(1), Failure Analysis of Hawsers on BOBO Class MSC Ships at Tinian on 7

December 1986). This is a sudden change in wind speed that is usually associatedwith a change in wind direction (Wind Effects on Structures, Simiu and Scanlan, 1996).The key problems with this phenomena are: (1) high mooring dynamic loads can be

produced in a wind gust front, (2) there is often little warning, (3) little is known aboutwind gust fronts, and (4) no design criteria for these events have been established.

A study of Guam Agana National Air Station (NAS) wind records was performed toobtain some statistics of wind gust fronts (National Climatic Data Center (NCDC), LetterReport E/CC31:MJC, 1987). The 4.5 years of records analyzed from 1982 through1986 showed approximately 500 cases of sudden wind speed change, which wereassociated with a shift in wind direction. These wind shifts predominately occurred in 1

minute or less and never took longer than 2 minutes to reach maximum wind speed.Figure 3-7 shows sudden changes in wind speed and direction that occurred over a 2-1/2 day period in October 1982. These wind gust fronts seemed to be associated with anearby typhoon.

Table 3-13 gives the joint distribution of wind shifts in terms of the amount the increasein wind speed and the wind direction change. Approximately 60 percent of the windgust fronts from 1982 through 1986 had wind direction changes in the 30-degree range,as shown in Figure 3-8.

Based on the Guam observations, the initial wind speed in a wind gust front ranges

from 0 to 75 percent of the maximum wind speed, as shown in Figure 3-9. On theaverage, the initial wind speed was 48 percent of the maximum in the 4.5-year samplefrom Guam (NCDC, 1987).

Simiu and Scanlan (1996) report wind gust front increases in wind speed ranging from 3m/sec to 30 m/sec (i.e., 6 to 60 knots). Figure 3-10 shows the distribution of gust frontwinds from the 4.5-year sample from 1982 through 1986 on Guam. This figure showsthe probability of exceedence on the x-axis in a logarithmic format. The square of thewind gust front speed maximums was plotted on the y-axis, since wind force isproportional to wind speed squared. Figure 3-10 provides a sample of the maximumwind gust front distribution for a relatively short period at one site. Those wind gust

fronts that occurred when a typhoon was nearby are identified with an H. It can beseen that the majority of the higher gust front maximums were associated withtyphoons. Also, the typhoon gust front wind speed maxima seem to follow a differentdistribution that the gust front maxima associated with rain and thunderstorms (seeFigure 3-10).

Effects of winds and wind gusts are shown in the examples in Chapter 8 of this UFC.

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Figure 3-7. Sample Wind Gust Fronts on Guam, 2-4 October 1982

0

5

10

15

20

25

30

35

40

45

0 12 24 36 48 60

TIME, (Hours; Start 02 Oct 82)

WINDSPEED(knots)

0

5

10

15

20

WINDSPEED(m/s)

Wind Dir.Shift (deg)=

40

40 4040

30

30

40

50

20

40

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Table 3-13. Sample Dist ribution of Wind Gust Fronts on Guam (Agana NAS) from1982 to 1986

NUMBER OF OBSERVATIONS

WIND SPEED CHANGE WIND DIRECTION CHANGE

(knots) (m/s)

MIN. MAX. MIN. MAX. 20 30 40 50 60 70 80 90deg deg deg deg deg deg deg deg

6 10 3.1 5.1 28 241 66 30 4 2

11 15 5.7 7.7 8 42 18 13 5 3 1 1

16 20 8.2 10.3 6 7 3 2 2

21 25 10.8 12.9 3 2 1

26 30 13.4 15.4 1

0

10

20

30

40

50

60

20 30 40 50 60 70 80 90

WIND ANGLE CHANGE (deg)

%OFSHIFTS

Percent of Observations

CLOCKWISE 62%

COUNTERCLOCKWISE 38%

Figure 3-8. Distribution of Guam Wind Gust Front Wind Angle Changes

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Figure 3-9. Initial Versus Maximum Wind Speeds for Wind Gust Fronts

0

5

10

15

20

25

0 5 10 15 20 25

MAX WIND SPEED (m/s)

INITIALWINDSPEE

D(m/s)

48%

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Figure 3-10. Wind Gust Front Maxima on Guam 1982-1986

0

100

200

300

400

500

600

0.1 1.0 10.0 100.0

PROBABILITY OF EXCEEDENCE

MAXWINDSPEEDSQUA

RED(m/s)2

H

H H

H

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3-8.3 Storms. Table 3-14 gives environmental parameters for standard storms.

Table 3-14. Storm Parameters

(a) Tropical Storms

LOWER WIND SPEED UPPER WIND SPEED

Storm (m/s) (mph) (knts) (m/s) (mph) (knts)

TROPICALDEPRESSION

9.8 22 19 16.5 37 32

TROPICAL STORM 17.0 38 33 32.6 73 63

HURRICANE 33.1 74 64 - - -

(b) Saffier-Simpson Hurricane Scale

WIND SPEED RANGE OPEN COAST STORM SURGE RANGELOWER UPPER LOWER UPPER

CATE-GORY

(m/s) (mph) (m/s) (mph) (m) (ft) (m) (ft)

1 33.1 74 42.5 95 1.22 4 1.52 5

2 42.9 96 49.2 110 1.83 6 2.44 8

3 49.6 111 58.1 130 2.74 9 3.66 12

4 58.6 131 69.3 155 3.96 13 5.49 18

5 69.7 156 - - 5.79 19 - -

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Table 3-14. (continued) Storm Parameters

(c) Beaufort Wind Force*

LOWER WIND SPEED UPPER WIND SPEEDBEAUFORT WINDFORCE/DESCRIPTION

(m/s) (mph) (knts) (m/s) (mph) (knts)

0 CALM 0.0 0 0 0.5 1 1

1 LIGHT AIRS 0.5 1 1 1.5 4 3

2 LIGHT BREEZE 2.1 5 4 3.1 7 6

3 GENTLE GREEZE 3.6 8 7 5.1 12 10

4 MODERATEBREEZE

5.7 13 11 8.2 18 16

5 FRESH BREEZE 8.8 20 17 10.8 24 216 STRONG BREEZE 11.3 25 22 13.9 31 27

7 MODERATE GALE 14.4 32 28 17.0 38 33

8 FRESH GALE 17.5 39 34 20.6 46 40

9 STRONG GALE 21.1 47 41 24.2 54 47

10 WHOLE GALE 24.7 55 48 28.3 63 55

11 STORM 28.8 65 56 32.4 73 63

12 HURRICANE 32.9 74 64 36.6 82 71

*AfterHandbook of Ocean and Underwater Engineers,Myers et al. (1969). The above table should be used with caution,

because design conditions for a specific site could vary from the values shown.

(d) World Meteorological Organization Sea State Scale

SEA STATESign. Wave Height(ft) [m]

Sustained Wind Speed(knts) [m/s]

ModalWavePeriodRange(sec)

0 CALM/GLASSY NONE NONE -

1 RIPPLED 0-0.3 [0-0.1] 0-6 [0-3] -

2 SMOOTH 0.3-1.6 [0.1-0.5] 7-10 [3.6-5.1] 3-153 SLIGHT 1.6-4.1 [0.5-1.2] 11-16 [5.7-8.2] 3-15.5

4 MODERATE 4.1-8.2 [1.2-2.5] 17-21 [8.7-10.8] 6-16

5 ROUGH 8.2-13.1 [2.5-4.0] 22-27 [11.3-13.9] 7-16.5

6 VERY ROUGH 13.1-19.7 [4.0-6.0] 28-47 [14.4-24.2] 9-17

7 HIGH 19.7-29.5 [6.0-9.0] 48-55 [24.7-28.3] 10-18

8 VERY HIGH 29.5-45.5[9.0-13.9] 56-63 [28.8-32.4] 13-19

9 PHENOMENAL >45.5 [>13.9] >63 [>32.4] 18-24

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3-8.4 Currents. The magnitude and direction of currents in harbors andnearshore areas are in most cases a function of location and time. Astronomical tides,river discharges, wind-driven currents, and other factors can influence currents. Forexample, wind-driven currents are surface currents that result from the stress exerted

by the wind on the sea surface. Wind-driven currents generally attain a mean velocityof approximately 3 to 5 percent of the mean wind speed at 10 meters (33 feet) abovethe sea surface. The magnitude of this current strongly decreases with depth.

Currents can be very site specific, so it is recommended that currents be measured atthe design site and combined with other information available to define the designcurrent conditions.

3-8.5 Water Levels. At most sites some standard datum, such as mean lowwater (MLW) or mean lower low water (MLLW), is established by formal methods.Water levels are then referenced to this datum. The water level in most harbors is then

a function of time. Factors influencing water levels include astronomical tides, stormsurges, river discharges, winds, seiches, and other factors.

The design range in water levels at the site must be considered in the design process.

3-8.6 Waves. Most DOD moorings are wisely located in harbors to helpminimize wave effects. However, waves can be important to mooring designs in somecases. The two primary wave categories of interest are:

a) Wind waves. Wind waves can be locally generated or can be windwaves or swell entering the harbor entrance(s). Small vessels are

especially susceptible to wind waves.

b) Long waves. These can be due to surf beat, harbor seiching, or othereffects.

Ship waves may be important in some cases. The response of a moored vessel towave forcing includes:

a) A steady mean force.

b) First order response, where the vessel responds to each wave, and

c) Second order response, where some natural long period mode ofship/mooring motion, which usually has little damping, is forced by the group or othernature of the waves.

If any of these effects are important to a given mooring design, then a six-degree-of-freedom dynamic of the system generally needs to be considered in design. Someguidance on safe wave limits for moored manned small craft is given in Table 3-8(a).

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3-8.7 Water Depths. The bathymetry of a site may be complex, depending on

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